1. Nuclear Science and Engineering Division, Argonne National Laboratory, Argonne, Illinois 60439, USA
2. Department of Electrical and Computer Engineering, Illinois Institute of Technology, Chicago, Illinois 60616, USA
3. Department of Nuclear Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
4. Department of Physics, University of California Berkeley, Berkeley, California 94720, USA
5. Westinghouse Electric Company, Hopkins, South Carolina 29061, USA